Technical Field
[0001] The present application relates to a pressure-sensitive adhesive composition for
a foldable display and a use thereof.
Background Art
[0002] Recently, with the development of display related technologies, display devices that
can be deformed at the use stage, such as folding, winding in a roll form, or stretching
like a rubber band are being studied and developed. Since these displays can be modified
into various forms, it is possible to satisfy both demands for enlargement of the
display at the use stage and miniaturization of the display for carrying.
[0003] The deformable display device can be modified in various forms in accordance with
the requirements of the user or depending on the needs of situations where the display
device is used, as well as capable of being transformed into a predetermined form.
Therefore, it is necessary to recognize the deformed shape of the display and to control
the display device in accordance with the recognized shape.
[0004] On the other hand, since the deformable display device has a problem that each of
constitutions of the display device is damaged according to the modification, each
of the constitutions of the display device must satisfy folding reliability and stability.
[Prior Art Documents]
[Patent Documents]
[0005] Patent Document 1: Korean Laid-Open Patent Publication No.
2015-0011230 A KR20160083583A discloses a composition for an adhesive for a foldable device comprising a linear
silicone which can be blended with an MQ resin.
Disclosure
Technical Problem
[0006] The present application provides a pressure-sensitive adhesive composition for a
foldable display and a use thereof.
[0007] The present application provides a pressure-sensitive adhesive composition for a
foldable display having excellent bending reliability by satisfying a storage elastic
modulus in a predetermined range over a wide temperature interval, for example, a
temperature interval of -40°C to 90°C.
[0008] The present application also provides a foldable display comprising a pressure-sensitive
adhesive layer having excellent adhesive force and cohesive force, while having bending
reliability suitable for a foldable display, and a method for manufacturing the same.
Technical Solution
[0009] The present application relates to a pressure-sensitive adhesive composition for
a foldable display and a use thereof.
[0010] The pressure-sensitive adhesive composition according to the present invention has
a storage elastic modulus of not more than 5.0 x 10
6 Pa after curing over a wide temperature interval, for example, a temperature interval
of -40°C to 90°C and thus has physical properties suitable for use in a foldable display.
[0011] In addition, the pressure-sensitive adhesive composition according to the present
application comprises a predetermined additive to realize high cohesive force and
adhesive force, thereby being capable of overcoming a problem in a pressure-sensitive
adhesive having a low pressure-sensitive adhesive force, for example, a low adhesive
force problem.
[0012] Such a pressure-sensitive adhesive composition is cured, for example, to form a pressure-sensitive
adhesive layer, where the pressure-sensitive adhesive layer is contained in a foldable
display, for example, formed on a base film and may exist on one side or both sides
of a polarizing plate.
[0013] In the present application, the term "foldable display" may mean a flexible display
having a radius of curvature in a folded portion of less than 5 mm by being designed
such that it can be repeatedly folded and spread like a paper.
[0014] The pressure-sensitive adhesive applied to the foldable display must satisfy bending
reliability, unlike conventional pressure-sensitive adhesives, and in order for such
bending reliability to be excellent, rheologic physical properties, for example, a
storage elastic modulus should be maintained within an appropriate range over the
temperature range in which an actual foldable display can be used.
[0015] However, in order to maintain the storage elastic modulus within an appropriate range
for securing the bending reliability, the content of the substance imparting adhesive
force should be reduced; but in this case, there is a problem that the adhesive force
of the pressure-sensitive adhesive itself decreases.
[0016] Thus, the pressure-sensitive adhesive composition according to the present invention
comprises a predetermined additive, together with a silicone pressure-sensitive adhesive
in which a variation width of the storage elastic modulus in the commercial temperature
range is minimized by controlling the content of an MQ resin that imparts a pressure-sensitive
adhesive property and appropriately designing the structure of silicone gum.
[0017] Accordingly, the pressure-sensitive adhesive composition according to the present
invention maintains the storage elastic modulus within an appropriate range, thereby
not only securing folding reliability required in the foldable display, but also being
capable of having excellent adhesive force and cohesive force.
[0018] That is, the present application relates to a pressure-sensitive adhesive composition
for a foldable display comprising: a first pressure-sensitive adhesive; a second pressure-sensitive
adhesive; and any one additive selected from the group consisting of a borane compound,
a borate compound and a mixture thereof.
[0019] The pressure-sensitive adhesive composition for a foldable display has a peel force
on a glass substrate of 0.00772 N/mm (20 gf/in) or more, as measured at a peel rate
of 0.3 m/min and a peel angle of 180 degrees after curing.
[0020] The first pressure-sensitive adhesive comprises a first silicone gum and a first
MQ resin and has a peel force on a glass substrate of 0.00386 N/mm (10 gf/in) or less,
as measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees.
[0021] The first pressure-sensitive adhesive is a low pressure-sensitive adhesive component
having a relatively low pressure-sensitive adhesive force, and comprises a first silicone
gum.
[0022] The term "silicone gum" herein is commonly called a polyorganosiloxane compound ordinarily
contained in a silicone-based pressure-sensitive adhesive, which can play a role of
imparting a constant storage elastic modulus and cohesive force to the pressure-sensitive
adhesive composition.
[0023] In one example, the first silicone gum may be represented by Formula 1 below.
[0024] In Formula 1 above, R
1 and R
6 are each independently a silyl group or silanol group with or without an alkyl group,
an alkenyl group or an aryl group, R
2 to R
5 are each independently an alkyl group, an alkenyl group or an aryl group, and n and
m are each independently an integer in a range of 1 to 10,000.
[0025] In the present application, the term "alkyl group" may mean an alkyl group having
1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms,
1 to 6 carbon atoms or 1 to 4 carbon atoms, unless otherwise specified. The alkyl
group may be linear, branched or cyclic. The alkyl group can be exemplified by a linear
or branched alkyl group such as a methyl group, an ethyl group, an n-propyl group,
an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a t-butyl
group, an n-pentyl group, an isopentyl group, a neopentyl group, an n-hexyl group,
an n-heptyl group or an n-octyl group, or a cycloalkyl group such as a cyclobutyl
group, a cyclopentyl group, a cyclohexyl group or a cycloheptyl group, and the like.
In addition, the alkyl group may be optionally substituted with one or more substituents.
[0026] In the present application, the term "alkenyl group" may mean an alkenyl group having
2 to 20 carbon atoms, 2 to 16 carbon atoms, 2 to 12 carbon atoms, 2 to 8 carbon atoms,
2 to 6 carbon atoms, or 2 to 4 carbon atoms, unless otherwise specified. The alkenyl
group may be linear, branched or cyclic. The alkenyl group can be exemplified by a
vinyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl group, a 2-butenyl
group or a 3-butenyl group, and the like. Also, the alkenyl group may be optionally
substituted with one or more substituents.
[0027] In the present application, the term "aryl group" may mean a monovalent residue derived
from a compound comprising a benzene ring or a structure in which two or more benzene
rings are condensed or bonded, or a derivative thereof, unless otherwise specified.
In the range of the aryl group, not only a functional group commonly called an aryl
group, but also a so-called aralkyl group or arylalkyl group, and the like can be
included. The aryl group may be, for example, an aryl group having 6 to 25 carbon
atoms, 6 to 21 carbon atoms, 6 to 18 carbon atoms, or 6 to 12 carbon atoms. The aryl
group can be exemplified by a phenyl group, a phenoxy group, a phenoxyphenyl group,
a phenoxybenzyl group, a dichlorophenyl group, a chlorophenyl group, a phenylethyl
group, a phenylpropyl group, a benzyl group, a tolyl group, a xylyl group or a naphthyl
group, and the like. In addition, the aryl group may be optionally substituted with
one or more substituents.
[0028] In the present application, the term "silanol group" means a functional group comprising
Si-OH units.
[0029] In the present application, the term "silyl group" means a generic term of a functional
group comprising silicon atoms.
[0030] In the present application, a specific functional group, for example, the substituent
which may be substituted in the alkyl group, alkenyl group or aryl group can be exemplified
by an alkyl group, an alkoxy group, an alkenyl group, an epoxy group, a cyano group,
a thiol group, a carboxyl group, an acryloyl group, a methacryloyl group, an acryloyloxy
group, a methacryloyloxy group or aryl group, and the like, but is not limited thereto.
[0031] The first silicone gum may have, for example, a number average molecular weight in
a range of 400,000 to 800,000. Within the range of the number average molecular weight,
it is possible to provide a pressure-sensitive adhesive composition preventing a rapid
change in storage elastic modulus and having an appropriate cohesive force.
[0032] Here, the number average molecular weight may be a value measured by a known measuring
method using gel permeation chromatography (GPC).
[0033] In another example, the silicone gum may have a number average molecular weight in
the range of 500,000 to 800,000 or 700,000 to 800,000.
[0034] The first silicone gum may also have a suitable cross-linkable functional group to
have a good cross-linking degree.
[0035] In one example, the first silicone gum may have a content of a cross-linkable functional
group, for example, a vinyl group in a range of 0.5 mol% to 1.5 mol% or 0.5 mol% to
1 mol%. Within the content range of the cross-linkable functional group as above,
it is possible to have a good cross-linking degree and to secure appropriate pressure-sensitive
adhesive force and cohesive force.
[0036] The first pressure-sensitive adhesive may also comprise an MQ resin.
[0037] Here, the term "MQ resin" also means a silicone compound having a three-dimensional
reticular steric molecular structure comprising a monofunctional siloxane unit (hereinafter,
referred to as "M unit") and a tetrafunctional siloxane unit (hereinafter, referred
to as "Q unit"). In addition, the MQ resin may further comprise other bifunctional
siloxane units (hereinafter, referred to as "D units") or trifunctional siloxane units
(hereinafter, referred to as "T units").
[0038] Here, the M unit means a unit represented by a formula (R
3SiO
1/2) in the industry; the D unit means a unit represented by a formula (R
2SiO
2/2) in the industry; the T unit means a unit represented by a formula (R
2SiO
3/2) in the industry; and the "Q unit" means a unit represented by a formula (SiO
4/2). Here, R means a functional group bonded to a silicon atom (Si).
[0039] The MQ resin plays a role of imparting pressure-sensitive adhesive force into the
pressure-sensitive adhesive, where the first pressure-sensitive adhesive is a low
pressure-sensitive adhesive having a relatively low peel force on a glass substrate,
so that it may have a very low content of MQ resin over the second pressure-sensitive
adhesive.
[0040] In one example, the first pressure-sensitive adhesive may comprise the first MQ resin
in a content of less than 5 wt%. If the content of the first MQ resin is 5 wt% or
more, the pressure-sensitive adhesive force may be excessively increased and the storage
elastic modulus may be changed radically, which is not preferable.
[0041] In another example, the first pressure-sensitive adhesive may comprise the first
MQ resin in a content of less than 4 wt%, less than 3 wt%, less than 2 wt%, or less
than 1 wt%. The upper limit value of the first MQ resin content may be, for example,
0.0001 wt% or more, 0.001 wt% or more, or 0.01 wt% or more.
[0042] In a specific example, the first pressure-sensitive adhesive may comprise 0.0001
to 5 parts by weight of the first MQ resin relative to 100 parts by weight of the
first silicone gum. In another example, it may comprise 0.001 to 4.5 parts by weight
or 0.01 to 4 parts by weight of the first MQ resin.
[0043] The first MQ resin may be represented by, for example, Formula 2 below, but is not
limited thereto.
[0044] In Formula 2 above, R is hydrogen, a monovalent hydrocarbon group, or an alkenyl
group.
[0045] The monovalent hydrocarbon group can be exemplified by an alkyl group, an aliphatic
cyclic group or an aromatic cyclic group, and the like.
[0046] More specifically, the alkyl group can be exemplified by an alkyl group such as methyl,
ethyl, propyl or pentyl, and the aliphatic cyclic group can be exemplified by cyclohexyl
or the like, and the aromatic cyclic group can be exemplified by phenyl, tolyl, xylyl
or benzyl, and the like, without being limited thereto.
[0047] Furthermore, the alkenyl group can be exemplified by vinyl, allyl, butenyl, hexenyl
or cyclohexenyl, and the like.
[0048] Meanwhile, the monovalent hydrocarbon group or the alkenyl group may exist in a radical
form.
[0049] The first MQ resin may further comprise, for example, a D unit or a T unit, where
it is preferred that the ratio of the D unit and the T unit further included is less
than 5 mol%.
[0050] For example, the first MQ resin may have a ratio of the M unit to the Q unit (M:
Q) in a range of 0.6: 1 to 1.7: 1 or 0.7: 1 to 1: 1. When the M unit is less than
0.6 relative to the Q unit, the initial pressure-sensitive adhesive force may be lowered,
and when it exceeds 1.7, the cohesive force may be lowered, which is not preferable.
[0051] The first MQ resin may comprise a silanol group, where the content of the silanol
group may be, for example, in the range of 0.1 mol% to 8 mol% or 0.2 mol% to 5 mol%.
When the content of the silanol group is less than 0.1 mol%, the cross-linking density
is lowered and the cohesive force is lowered, which is not preferable, and when it
exceeds 8 mol%, the adhesive force is lowered, which is not preferable.
[0052] The first MQ resin may comprise, for example, the hydrogen atom in a ratio of 1 to
3 mol% relative to the entire functional group bonded to the silicon atom. By controlling
the ratio of the hydrogen atom within the above range, it is possible to prevent an
uncured problem, or deterioration of storage stability or the like.
[0053] The first MQ resin may have, for example, a number average molecular weight in the
range of 3,000 to 7,000. When the MQ resin having a number average molecular weight
within the above range is used, excellent cohesive force and adhesive force can be
achieved.
[0054] The above-described first pressure-sensitive adhesive is a low pressure-sensitive
adhesive having a low adhesive force, and has a peel force on a glass substrate of
10 gf/in or less, as measured at a peel rate of 0.3 m/min and a peel angle of 180
degrees. In another example, the peel force on a glass substrate may be 9 gf/in or
less, 8 gf/in or less, 7 gf/in or less, 6 gf/in or less, 5 gf/in or less, 4 gf/in
or less, or 3 gf/in or less. The lower limit value of the peel force of the first
pressure-sensitive adhesive on a glass substrate is not particularly limited, but
may be 0.1 gf/in or more, for example. 1 gf/in = 0.000386 N/mm.
[0055] The first pressure-sensitive adhesive is included in the composition in a range of
5 wt% to 50 wt% relative to the total solid content of the composition. In another
example, the first pressure-sensitive adhesive may be included in the composition
in a range of 8 wt% to 45 wt% or 10 wt% to 30 wt% relative to the total solid content
of the composition.
[0056] The pressure-sensitive adhesive composition of the present application further comprises
a second pressure-sensitive adhesive. The second pressure-sensitive adhesive has a
peel force on a glass substrate of 0.0772 to 0.1544 N/mm (200 to 400 gf/in) as measured
at a peel rate of 0.3 m/min and a peel angle of 180 degrees.
[0057] The second pressure-sensitive adhesive is a high pressure-sensitive adhesive component
having a relatively high pressure-sensitive adhesive force as compared with the first
pressure-sensitive adhesive, and has a high peel force on a glass substrate.
[0058] The second pressure-sensitive adhesive comprises a second silicone gum and a second
MQ resin.
[0059] The second pressure-sensitive adhesive may have a storage elastic modulus measured
at -40°C of 10
7 Pa or less. When the second pressure-sensitive adhesive having the storage elastic
modulus as described above is mixed with the first pressure-sensitive adhesive, a
pressure-sensitive adhesive composition having a storage elastic modulus after curing
over a temperature interval of -40°C to 90°C, of 5.0 x 10
6 Pa or less, can be provided.
[0060] The second silicone gum may be the same as or different from the above-described
first silicone gum.
[0061] In one example, the second silicone gum may have a structure different from the above-described
first silicone gum.
[0062] More specifically, the second silicone gum may have a low cross-linking degree and
a high cross-linking density in order to secure the property that the second pressure-sensitive
adhesive has high pressure-sensitive adhesive force.
[0063] In one example, the second silicone gum may be linear polydimethylsiloxane comprising
hydroxy groups at both ends. The linear polydimethylsiloxane having hydroxy groups
at both ends means polydimethylsiloxane having a linear structure in which in Formula
1 above, R
2 to R
5 are all methyl groups and R
1 and R
6 are Si(CH
3)
2OH.
[0064] The linear polydimethylsiloxane may be, for example, one that the hydroxy group is
in a range of 0.5 mol% to 5 mol% or 1 mol% to 4 mol% relative to the total methyl
groups contained in the polydimethylsiloxane. When the hydroxy group is in the above
range, it is possible to prevent a curing problem, such as the uncured, by achieving
an appropriate cross-linking degree, and to improve long-term properties such as a
storage property.
[0065] The second silicone gum may also have a number average molecular weight in the range
of 500,000 to 1,000,000. In another example, the second silicone gum may have a number
average molecular weight in the range of 500,000 to 900,000 or 700,000 to 900,000.
When the silicone gum having the number average molecular weight within the above
range is used, it is possible to provide a pressure-sensitive adhesive composition
preventing a rapid change of a storage elastic modulus over an interval from a low
temperature of 40°C to a high temperature of 90°C and having an appropriate cohesive
force.
[0066] The second silicone gum may have an appropriate viscosity in consideration of pressure-sensitive
adhesive force, workability and reactivity with the MQ resin, and the like.
[0067] The second silicone gum may have, for example, a viscosity measured under a condition
of 25°C and 50% relative humidity in a range of 1,000,000 cP to 100,000,000 cP. In
another example, the second silicone gum may have a viscosity measured under a condition
of 25°C and 50% relative humidity in the range of 1,500,000 cP to 70,000,000 cP. If
the viscosity is less than 1,000,000 cP, the reactivity or the pressure-sensitive
adhesive force may be lowered, and if the viscosity exceeds 100,000,000 cP, the workability
may be significantly lowered.
[0068] The second MQ resin may be the same as or different from the above-described first
MQ resin.
[0069] The second MQ resin is a component that provides the adhesive force and cohesive
force of the pressure-sensitive adhesive, like the first MQ resin, and a constitution
that can change the storage elastic modulus according to the content thereof.
[0070] On the other hand, the second pressure-sensitive adhesive has a high pressure-sensitive
adhesive property, and may have the MQ resin content higher than that of the first
pressure-sensitive adhesive. However, when the content of the second MQ resin is too
large, the storage elastic modulus of the second adhesive may exceed 10
7 Pa at -40°C, so that the second adhesive may comprise the second MQ resin within
an appropriate range.
[0071] In one example, the second pressure-sensitive adhesive may comprise the second MQ
resin in a content of 40 wt% or less. In another example, the second pressure-sensitive
adhesive may comprise the second MQ resin in a ratio of 38 wt% or less, 36 wt% or
less, 34 wt% or less, 32 wt% or less, or 30 wt% or less, and preferably, it may be
36 wt% or less. The lower limit value of the second MQ resin content may be, for example,
5 wt% or more, 10 wt% or more, or 15 wt% or more. When the content of the second MQ
resin in the second pressure-sensitive adhesive is controlled within the above range,
it is possible to provide a second pressure-sensitive adhesive having a storage elastic
modulus at -40°C of 1.0 x 10
7 Pa or less.
[0072] In a specific example, the second pressure-sensitive adhesive may comprise 60 to
95 parts by weight of a second silicone gum and 5 to 40 parts by weight of a second
MQ resin. In another example, the second pressure-sensitive adhesive comprises 64
to 90 parts by weight of a second silicone gum and 10 to 36 parts by weight of a second
MQ resin, or 70 to 85 parts by weight of a second silicone gum and 25 to 30 parts
by weight of a second MQ resin.
[0073] The pressure-sensitive adhesive composition of the present application comprises
the above-described first pressure-sensitive adhesive and second pressure-sensitive
adhesive in a predetermined ratio.
[0074] In one example, the pressure-sensitive adhesive composition comprises the first pressure-sensitive
adhesive in a range of 5 wt% to 50 wt% relative to the total solid content of the
composition. In another example, the pressure-sensitive adhesive composition may comprise
the first pressure-sensitive adhesive in a range of 8 wt% to 40 wt% or 9 wt% to 35
wt% of the total solid content.
[0075] The content of the second pressure-sensitive adhesive can be changed depending on
the content of the first pressure-sensitive adhesive in the pressure-sensitive adhesive
composition, and so the second pressure-sensitive adhesive is included in the pressure-sensitive
adhesive composition in a content within the range of 50 wt% to 95 wt%, for example
55 wt% to 94 wt%, or 70 wt% to 90 wt%, relative to the total solid content of the
composition.
[0076] The pressure-sensitive adhesive composition according to the present application
also comprises an additive for reinforcing the low adhesive force of the silicone
pressure-sensitive adhesive as above.
[0077] That is, the pressure-sensitive adhesive composition for a foldable display according
to the present application comprises, together with the silicone pressure-sensitive
adhesive, any one additive selected from the group consisting of a borane compound,
a borate compound and a mixture thereof.
[0078] Due to the addition of the additive, the pressure-sensitive adhesive composition
for a foldable display can be provided, which has excellent adhesive property, and
for example, a peel force on a glass substrate of 0.00772 N/mm (20 gf/in) or more,
as measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees after curing.
[0079] The borane compound in the additive may be represented by, for example, Formula 3.
[0080] In Formula 3, R
4 to R
6 are each independently hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms,
or a silyl group.
[0081] The borate compound in the additive may be represented by Formula 4 below.
[0082] In Formula 4, R
7 to R
9 are each independently hydrogen, halogen, an alkyl group having 1 to 6 carbon atoms,
or a silyl group.
[0083] In a more specific example, the borane compound or the borate compound may be exemplified
by triethyl borate, ethyl borane or methyl borane, and the like, but is not limited
thereto, where the borane compound or the borate compound to play a role in improving
the adhesive physical property of the silicone pressure-sensitive adhesive may be
used without limitation.
[0084] The additive may be contained in the pressure-sensitive adhesive composition in such
an amount that can secure the desired adhesive force of the pressure-sensitive adhesive
by improving the adhesive physical property of the silicone pressure-sensitive adhesive.
[0085] In one example, the additive may be included in the pressure-sensitive adhesive composition
in a range of 0.01 to 5 wt% relative to the total solid content of the pressure-sensitive
adhesive composition. If the content of the additive exceeds 5 wt%, the adhesive force
may be excessively increased or an aggregation phenomenon between the additives may
occur, and if the content of the additive is less than 0.01 wt%, the object of improving
the adhesive physical property may not be achieved.
[0086] In another example, the additive may be included in the pressure-sensitive adhesive
composition in a range of 0.05 to 4 wt% or 0.1 to 3 wt%, relative to the total solid
content of the pressure-sensitive adhesive composition.
[0087] The pressure-sensitive adhesive composition for a foldable display according to the
present application may further comprise an organic solvent.
[0088] The organic solvent has solubility in the silicone gum and the MQ resin, which can
be exemplified by, for example, a saturated hydrocarbon-based organic solvent, a halogenated
hydrocarbon solvent, and an aromatic hydrocarbon-based organic solvent.
[0089] The saturated hydrocarbon-based organic solvent can be exemplified by, for example,
pentane, isopentane, cyclopentane, hexane, cyclohexane, heptane, isoheptane, cycloheptane,
octane, isooctane or cyclooctane, and the like; the halogenated hydrocarbon solvent
can be exemplified by trichloroethane or chloroform, and the like; and the aromatic
hydrocarbon-based organic solvent can be exemplified by, for example, benzene, xylene
or toluene, and the like, but are not limited thereto.
[0090] The pressure-sensitive adhesive composition for a foldable display of the present
application can have a low storage elastic modulus characteristic over a temperature
interval of 40°C to 90°C by comprising the first and second pressure-sensitive adhesives,
and can also secure excellent adhesive force and cohesive force due to the additive.
[0091] In one example, the pressure-sensitive adhesive composition of the present application
may have a storage elastic modulus (G') of 5.0 x 10
6 Pa or less after curing within a temperature range of -40°C to 90°C.
[0092] The storage elastic modulus may be, for example, a value measured according to a
manual using a rheometer (Advanced Rheometric Expansion System, Ta Instruments) under
a condition of a frequency of 0.1 rad/s to 100 rad/s and a strain rate of 10% or less.
[0093] In one example, the storage elastic modulus may be measured using a G2 series rheometer
from TA instruments under a condition of a frequency of 6.2 rad/s and a strain rate
of 10% or less depending on temperatures, while varying the temperature from -40°C
to 90°C, and derived.
[0094] In addition, the lower limit value of the storage elastic modulus of the pressure-sensitive
adhesive composition after curing within the above temperature range may be, for example,
1.0 x 10
3 Pa.
[0095] In a more specific example, the pressure-sensitive adhesive composition of the present
application has a storage elastic modulus value in the range of 1.0 x 10
3 Pa to 5.0 x 10
6 Pa, 5.0 x 10
3 Pa to 3.0 x 10
6 Pa or 1.0 x 10
4 Pa to 1.0 x 10
6 Pa over a temperature interval of -40°C to 90°C. Within the above storage elastic
modulus range, it is possible to secure the superiority of the bending reliability
suitable for the foldable display.
[0096] In addition, as described above, the pressure-sensitive adhesive composition for
a foldable display has a peel force on a glass substrate of 0.00772 N/mm (20 gf/in)
or more, as measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees after
curing.
[0097] In another example, the pressure-sensitive adhesive composition for a foldable display
has a peel force on a glass substrate of 25 gf/in or more, 27 gf/in or more, 28 gf/in
or more, 29 gf/in or more, or 30 gf/in or more, as measured at a peel rate of 0.3
m/min and a peel angle of 180 degrees after curing, where 1 gf/in = 0.000386 N/mm.
[0098] The present application is also directed to a foldable display. The foldable display
of the present application can secure excellent bending reliability required for a
foldable display, as well as excellent cohesive force and adhesive force by comprising
the pressure-sensitive adhesive layer which is a cured product of the above-described
pressure-sensitive adhesive composition.
[0099] That is, the present application is directed to a foldable display comprising a pressure-sensitive
adhesive layer which is a cured product of a pressure-sensitive adhesive composition
for a foldable display attached to an adherend. The pressure-sensitive adhesive composition
comprises: a first pressure-sensitive adhesive; a second pressure-sensitive adhesive;
and any one additive selected from the group consisting of a borane compound, a borate
compound and a mixture thereof. Furthermore, the pressure-sensitive adhesive layer
has a peel force on a glass substrate of 0.007720 N/mm (20 gf/in) or more, as measured
at a peel rate of 0.3 m/min and a peel angle of 180 degrees.
[0100] The pressure-sensitive adhesive layer in the foldable display of the present application
is attached on the adherend.
[0101] The adherend may be, for example, a base film.
[0102] The base film may also be, for example, a transparent base film having a haze of
10% or less, or 5% or less, or may also be a colored base film having a haze of 30%
or more.
[0103] As the base film, for example, those formed from polyolefin such as polyethylene
or polypropylene; polyester such as polyethylene terephthalate and polyethylene naphthalate;
cellulose such as triacetylcellulose, diacetylcellulose, propionylcellulose, butylcellulose
or acetylcellulose; polyamide such as 6-nylon or 6,6-nylon; an acrylic polymer such
as polymethyl methacrylate; and an organic polymer such as polystyrene, polyvinyl
chloride, polyimide, polyvinyl alcohol, polycarbonate or ethylene vinyl alcohol can
be used, without being limited thereto.
[0104] The base film may also be one formed from one or a mixture of two or more of the
foregoing or a polymer, and may also be one having a structure in which a plurality
of layers are laminated.
[0105] The base film may be, for example, one whose surface has been modified. The surface
modification may be performed for the purpose of increasing the pressure-sensitive
adhesive force with the pressure-sensitive adhesive layer, and specifically, a treatment
method such as chemical treatment, corona discharge treatment, mechanical treatment,
ultraviolet (UV) treatment, active plasma treatment or glow discharge treatment may
be adopted, without being limited thereto.
[0106] In one example, when the adherend is a base film, the base film and the pressure-sensitive
adhesive layer may form covalent bonds via the silanol group contained in the pressure-sensitive
adhesive layer by the above surface treatment of the base film and a surface treatment
process of a pressure-sensitive adhesive layer to be described below.
[0107] That is, in the case of performing the surface treatment process of the base film,
a functional group such as -OH is induced on the base film, and the functional group
can help to firmly maintain bonding between the base film and the pressure-sensitive
adhesive layer as a whole, by forming a covalent bond with the silanol group.
[0108] Furthermore, the base film may comprise known additives, such as an antistatic agent,
an ultraviolet absorber, an infrared absorber, a plasticizer, a lubricant, a colorant,
an antioxidant or a flame retardant.
[0109] The pressure-sensitive adhesive layer may be, for example, one whose surface has
been modified. The surface modification can be carried out to maintain a firm adhesive
force with the adherend, for example, the base film. The surface modification method
may be appropriately adopted from the above-described methods for modifying the surface
of the base film.
[0110] Through the surface modification, a silanol group can be formed in the pressure-sensitive
adhesive layer, and the silanol group can form a covalent bond with a functional group
such as -OH on the base film.
[0111] By the surface treatment of the adherend and the adhesive layer as above, the adherend
and the pressure-sensitive adhesive layer can secure excellent adhesive force.
[0112] In one example, the pressure-sensitive adhesive layer included in the foldable display
may have a peel force on the adherend of 0.7720 N/mm (2000 gf/in) or more, as measured
at a peel rate of 0.3 m/min and a peel angle of 180 degrees.
[0113] In another example, the pressure-sensitive adhesive layer may have a peel force on
the adherend of 0.8494 N/mm (2200 gf/in) or more or 0.9266 N/ mm (2400 gf/in) or more,
as measured at a peel rate of 0.3 m/min and a peel angle of 180 degrees.
[0114] The foldable display according to the present application may further comprise a
polarizing plate, wherein the pressure-sensitive adhesive layer may be formed on one
or both sides of the polarizing plate.
[0115] As the method of forming the pressure-sensitive adhesive layer, for example, a method
of coating a composition comprising a first pressure-sensitive adhesive, a second
pressure-sensitive adhesive, an additive and other solvents, and the like on any support
and then curing it can be used.
[0116] The method of coating and curing is not particularly limited, and for example, may
comprise coating using a known method such as bar coating, gravure coating, reverse
roll coating, reverse gravure coating, slot die coating, comma coating, spray coating,
knife coating, die coating, dip coating, micro gravure coating or wire bar coating,
followed by curing with application of appropriate heat.
Advantageous Effects
[0117] The present application can provide a pressure-sensitive adhesive composition having
bending reliability suitable for being applied to a foldable display, and also having
excellent pressure-sensitive adhesive physical property and cohesive force, and a
use thereof.
Mode for Invention
[0118] Hereinafter, the pressure-sensitive adhesive composition for a foldable display according
to the present application and the display comprising the same will be described in
detail with reference to Examples and Comparative Examples, but the following examples
are only examples according to the present application, and thus do not limit the
technical idea of the present application.
[0119] The physical properties of the pressure-sensitive adhesive composition of the present
application were evaluated by the following methods.
1. Measurement of storage elastic modulus
[0120] A pressure-sensitive adhesive composition prepared in Examples and Comparative Examples
was coated between release films and cured, and then tailored to a size of 15 cm x
25 cm, and laminated several times to have a thickness of about 1 mm, after removing
the release film on one side. Subsequently, the laminate was tailored into a circle
having a diameter of 8 mm and compressed using glass, and then a sample was prepared
by allowing the laminate to stand overnight to improve wetting at the interfaces between
the layers and removing bubbles generated upon lamination. Subsequently, the sample
was placed on a parallel plate, the gap was adjusted, the zero point of Normal & Torque
was set, and the storage elastic modulus was measured after confirming stabilization
of Normal force.
(1) Measuring instruments and measuring conditions
[0121] Measuring instrument: ARES-RDA equipped with a forced convection oven, TA Instruments
Inc. (G2 series Rheometer)
(2) Measurement conditions
[0122] Geometry: 8 mm parallel plate
Interval: about 1 mm
Test type: dynamic strain frequency sweep
Strain = 0.1 [%]
Initial temperature: -40°C, final temperature: 90°C
Frequency: 6.2 rad/s
2. Peel force measurement
[0123] The pressure-sensitive adhesive layer prepared according to Examples and Comparative
Examples was attached to a glass substrate or a surface-treated PI base film as an
adherend and then aged under a condition of 50°C and 506625 Pa (5 atm) for 1 hour
or at room temperature for 3 days. After aging, the peel force was measured at a peel
rate of 0.3 m/min and a peel angle of 180 degrees at room temperature using a tensile
tester (Texture Analyzer). 1 gf/in = 0.000386 N/mm.
Example 1.
Preparation of pressure-sensitive adhesive composition (A1)
[0124] A first pressure-sensitive adhesive comprising a first polysiloxane gum with a vinyl
group content of 0.5 mol% and a number average molecular weight of about 600,000,
and about 0.001 wt% of a MQ resin with a structure of Formula 2 (R is an alkyl group
having 1 to 2 carbon atoms), and having a peel force on a glass substrate of about
2 gf/in, and a second pressure-sensitive adhesive comprising a second polysiloxane
silicone gum containing hyroxy groups at both ends and having a number average molecular
weight of 700,000, and about 38 wt% of the MQ resin, and having a peel force on a
glass substrate of about 337 gf/in were mixed with triethyl borate and a solvent,
but a pressure-sensitive adhesive composition (A1) was prepared by adjusting the content
of the first pressure-sensitive adhesive to about 10 wt% of the total solid content
of the composition and adjusting the content of triethyl borate to 1 wt% relative
to the total content of the composition.
Formation of pressure-sensitive adhesive layer (B1)
[0125] The pressure-sensitive adhesive composition (A1) was coated on the primer-treated
PET base material and cured to form a pressure-sensitive adhesive layer (B1), where
the pressure-sensitive adhesive layer (B1) was subjected to surface modification.
Example 2.
[0126] A pressure-sensitive adhesive composition (A2) was prepared in the same manner as
in Example 1, except that the content of triethyl borate was changed to 2 wt% relative
to the total solid content of the composition, and a pressure-sensitive adhesive layer
(B2) was formed using the same and subjected to surface modification.
Example 3.
[0127] A pressure-sensitive adhesive composition (A3) was prepared in the same manner as
in Example 1, except that the content of the first pressure-sensitive adhesive was
adjusted to about 30 wt% of the total solid content of the composition and the content
of triethyl borate was adjusted to 1 wt% relative to the total solid content of the
composition, and a pressure-sensitive adhesive layer (B3) was formed using the same
and subjected to surface modification.
Comparative Example 1.
[0128] A pressure-sensitive adhesive composition (A4) was prepared in the same manner as
in Example 1, except that triethyl borate was not included, and a pressure-sensitive
adhesive layer (B4) was formed using the same and subjected to surface modification.
Comparative Example 2.
[0129] A pressure-sensitive adhesive composition (A5) was prepared in the same manner as
in Example 3, except that triethyl borate was not included, and a pressure-sensitive
adhesive layer (B5) was formed using the same and subjected to surface modification.
Experimental Example 1 - Measurement of peel force on glass substrate or PI base film
[0130] The peel forces of the pressure-sensitive adhesive layers according to Examples 1
to 3 and Comparative Examples 1 and 2 on a glass substrate or a PI base film were
measured, and the results were shown in Table 1 below.
[Table 1] (1 gf/in = 0.000386 N/mm).
|
Example |
Comparative Example |
1 |
2 |
3 |
1 |
2 |
Adhesive force on glass substrate (gf/in) |
32 |
32 |
28 |
10 |
8 |
Adhesive force on PI base film (gf/in) |
2,737 |
2,666 |
2,400 |
44 |
22 |
[0131] As described in Table 1 above, it could be confirmed that when the pressure-sensitive
adhesive layers were formed using the pressure-sensitive adhesive compositions according
to Examples 1 to 3 of the present application, they had excellent adhesive forces
on the glass substrate or the PI base film, but in the case of the pressure-sensitive
adhesive layers according to Comparative Examples 1 and 2, they were not suitable
as a pressure-sensitive adhesive composition for a foldable display due to low pressure-sensitive
adhesive forces.
Experimental Example 2 - Measurement of storage elastic modulus
[0132] In order to examine the storage elastic modulus change rate depending on temperatures
after curing of the compositions according to Examples 1 to 3, the storage elastic
modulus at -40°C and 90°V was measured according to the above-described measuring
method using an ARES-RDA, an equipment of TA instruments, equipped with a forced convection
oven and the results were shown in Table 2.
[Table 2] (1 gf/in = 0.000386 N/mm).
|
Example 1 |
Example 2 |
Example 3 |
Storage elastic modulus at -40°C (Pa) |
1.8 x 105 Pa |
1.8 x 105 Pa |
1.8 x 105 Pa |
Storage elastic modulus at 90°C (Pa) |
1.1 x 105 Pa |
1.1 x 105 Pa |
1.7 x 105 Pa |
1. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige umfassend:
einen ersten druckempfindlichen Klebstoff, umfassend einen ersten Silikongummi und
mit einer Schälkraft auf einem Glassubstrat von 0,00386 N/mm (10 gf/in) oder weniger,
gemessen bei einer Schälrate von 0,3 m/min und einem Schälwinkel von 180°, wobei der
erste druckempfindliche Klebstoff in der Zusammensetzung in einer Menge von 5 bis
50 Gew.-%, bezogen auf den Gesamtfeststoffgehalt der Zusammensetzung, eingeschlossen
ist;
einen zweiten druckempfindlichen Klebstoff, umfassend einen zweiten Silikongummi und
ein zweites MQ-Harz mit einer Schälkraft auf einem Glassubstrat von 0,0772 N/mm (200
gf/in) bis 0,1544 N/mm (400 gf/in), gemessen bei einer Schälrate von 0,3 m/min und
einem Schälwinkel von 180°, wobei der zweite druckempfindliche Klebstoff in einer
Menge von 50 bis 95 Gew.-%, bezogen auf den Gesamtfeststoffgehalt der Zusammensetzung
umfasst ist; und
ein beliebiges Additiv, ausgewählt aus der Gruppe, bestehend aus einer Boranverbindung,
einer Boratverbindung und einem Gemisch davon;
wobei die Schälkraft wie in der Beschreibung angegeben gemessen wird.
2. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1,
wobei eine Schälkraft auf einem Glassubstrat, gemessen bei einer Schälrate von 0,3
m/min und einem Schälwinkel von 180°, 0,00772 N/mm (20 gf/in) oder mehr ist, wobei
die Schälkraft wie in der Beschreibung angegeben gemessen wird.
3. Druckempfindliche Zusammensetzung für eine faltbare Anzeige nach Anspruch 1, wobei
der erste oder zweite Silikongummi durch die unten angegebene Formel 1 dargestellt
ist:
wobei R
1 und R
6 jeweils unabhängig eine Silylgruppe oder Silanolgruppe mit oder ohne einer Alkenylgruppe
oder einer Arylgruppe sind, R
2 bis R
5 jeweils unabhängig eine Alkylgruppe, eine Alkenylgruppe oder eine Arylgruppe sind,
und n und m jeweils unabhängig eine ganze Zahl in einem Bereich von 1 bis 10.000 sind.
4. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1, wobei der erste druckempfindliche Klebstoff ein erstes MQ-Harz in einer Menge von
weniger als 5 Gew.-% umfasst.
5. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1,
wobei der erste Silikongummi ein Zahlmittel des Molekulargewichts in einem Bereich
von 400.000 bis 800.000 hat, bestimmt gemäß dem Verfahren wie in der Beschreibung
angegeben.
6. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1, wobei der erste Silikongummi einen Vinylgruppengehalt in einem Bereich von 0,5
bis 1 Mol% hat.
7. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1,
wobei der zweite druckempfindliche Klebstoff in einem Bereich von 5 Gew.-% bis 50
Gew.-%, bezogen auf den Gesamtfeststoffgehalt der Zusammensetzung,
enthalten ist.
8. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch,
wobei der zweite druckempfindliche Klebstoff das zweite MQ-Harz in einer Menge von
40 Gewichtsprozent oder weniger umfasst.
9. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1,
wobei der zweite Silikongummi ein lineares Polydimethylsiloxan ist, das Hydroxylgruppen
an beiden Enden enthält.
10. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1, wobei die Boranverbindung durch die unten angegebene Formel 3 dargestellt wird:
wobei R
4 bis R
6 jeweils unabhängig Wasserstoff, Halogen, eine Alkylgruppe mit 1 bis 6 Kohlenstoffatomen
oder eine Silylgruppe sind.
11. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1,
wobei die Boratverbindung durch die unten angegebene Formel 4 dargestellt wird:
wobei R
7 bis R
9 jeweils unabhängig voneinander Wasserstoff, Halogen, eine Alkylgruppe mit 1 bis 6
Kohlenstoffatomen oder eine Silylgruppe sind.
12. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1,
wobei das Additiv in einem Bereich von 0,01 bis 5 Gew.-%, bezogen auf den Gesamtfeststoffgehalt
der druckempfindlichen Klebstoffzusammensetzung enthalten ist.
13. Druckempfindliche Klebstoffzusammensetzung für eine faltbare Anzeige nach Anspruch
1,
wobei ein Speicherelastizitätsmodulus (G') nach Härten 5 x 106 Pa oder weniger innerhalb eines Temperaturbereichs von -40°C bis 90°C ist;
wobei der Speicherelastizitätsmodulus gemäß dem in der Beschreibung angegebenen Verfahren
gemessen wird.
14. Faltbare Anzeige umfassend eine druckempfindliche Klebstoffschicht, die ein gehärtetes
Produkt einer druckempfindlichen Klebstoffzusammensetzung für eine faltbare Anzeige
nach Anspruch 1 ist, angebracht an einer Klebefläche.
15. Faltbare Anzeige nach Anspruch 14, wobei die druckempfindliche Klebstoffschicht eine
Schälkraft auf der Klebefläche von 0,7721 N/mm (2000 gf/in) oder mehr hat, gemessen
bei einer Schälrate von 0,3 m/min und einem Schälwinkel von 180°, gemessen gemäß dem
Verfahren wie in der Beschreibung angegeben.